It is common to quantitatively measure the size and concentration of particulate contaminates in liquids, such as new and used oils, in order to determine various characteristics of the liquids. In samples of used oil, for instance, there are both “hard particles” that are targeted for measurement in terms of size and concentration, and similarly-sized “soft particles” that inhibit the accurate measurement of the hard particles. The presence of soft particles in a liquid sample is known to significantly elevate particle counts to the point where their presence compromises the validity of the count data obtained. It has been found, however, that the addition of a suitable diluent to oil samples, can substantially eliminate the interference of soft practices in obtaining accurate hard particle count data.
Hard particles in oil include without limitation, dirt and metal fragments, which have a serious impact on the life of equipment by accelerating wear and erosion. Such hard particles originate from a variety of sources, including generation from within an operating fluid system, ingress into the operating fluid system, or contamination that may occur during the storage and handling of new oils. Typically, “soft particles” include certain additives or additive by-products that are semi-insoluble or insoluble in oil, and other similar materials that are not known to directly increase wear and erosion within an operating system, such as, for example, air bubbles and water bubbles.
The measurement of such contaminants is particularly important in order to identify the potential problems with samples of new or used oils, to determine the characteristics of various types of new or used oils, and also to determine whether engines and/or machinery are introducing metal particles into used oil. More particularly, particle count results can be used to aid in assessing the capability of the filtration system responsible for cleaning oil or other fluid, determining if off-line recirculating filtration is needed to clean up the fluid system, or aiding in the decision of whether or not a fluid change is required. An abnormal particle count may trigger concerns of these possibilities, which can be confirmed by additional testing.
Fundamentally, in order to permit the calculation of useful and relevant data related to particles found in fluids, such as oil, the quantity of various sizes of contaminants needs to be determined. It is well known that in order to be useful, such measurement requires quantitative guidelines in order to meaningfully present the results. Accordingly, various standards are used for testing and reporting fluid cleanliness. Two such standards include the SAE Aerospace Standard (AS) and the ISO Code System. It has been found useful to group particle sizes into coded ranges in order to permit ready handling and manipulation of the data. The following table illustrates one such standard of measurement as per the SAE Aerospace Standard (AS) system, with the codes for each range given in the left-most column.
Cleanliness Classes for DifferentialParticle Counts (particles/100 ml)Size6 μm (c)14 μm(c)21 μm(c)38 μm(c)totototoCode14 μm(c)21 μm(c)38 μm(c)70 μm(c)>70 μm(c)0012622410025044820150089163121000178326132000356631124400071212622458000142525345861600028505069016732000570010121803286400011400202536064912800022800405072012810256000456008100144025611512000912001620028805121210240001824003240057601024
It is well known to use automated optical particle counters to quantitatively measure the size and concentration of particulate contaminants in samples of fluids, such as new and used oil. Commonly, such optical particle counters perform analysis based on the light extinction principle, using a laser beam passing through a liquid sample. Such optical particle counters are capable of recording the size and number of particles as they pass across a detector, and such equipment typically includes a sampling apparatus that automatically delivers a pre-determined volume of liquid specimen at a controlled flow rate to the optical sensing cell of the optical particle counter. Examples of prior art optical particle counters are taught in, amongst others, U.S. Pat. No. 5,426,501 (Hokanson et al.) issued Jun. 20, 1995, and U.S. Pat. No. 5,172,004 (Furuya) issued Dec. 15, 1992. Indeed, tests performed by such automated optical particle counters are considered by many to be the single most important test for oil analysis.
There are various well-known problems associated with the use of optical particle counters to test liquid samples, especially samples of oil. One of the two most fundamental problems is that of particle co-incidence. Particle co-incidence occurs when more than one particle is present in the optical sensing cell of the optical particle counter at the same time and a “large” particle is falsely detected rather than two (or more) smaller ones. It is well known that particle co-incidence causes inaccurate counting of the “hard particles” due to the presence of other type of particles, such as the “soft particles” in the liquid sample. Soft particles cause false high counts of particles in their size category, thus yielding false counts and an over-estimation of contamination levels across all sizes. Dilution of samples with a suitable diluent can reduce the probability of particle co-incidence.
Particle co-incidence can also occur due to the existence of air bubbles in the oil, thereby causing false positive readings. Bubbles can be caused by overly vigorous mixing or agitation of a liquid sample, which mixing may be necessary as part of the test procedure. Further, suspended or free water in the oil will generally be counted as particles.
Another fundamental problem associated with the use of optical particle counters to test liquid samples is that of the proper flow of high viscosity liquid samples. The forces required in order to develop the necessary pressure to rapidly achieve the required flow rate of the liquid samples through the optical sensing cell becomes quite significant, and even prohibitive. For this reason, it is extremely difficult to properly and accurately test high viscosity liquid samples in an optical particle counter without sample dilution using a suitable diluent.
In spite of the above stated advantages of using diluted oil samples for testing with optical particle counters, the vast majority of such testing is still carried out on undiluted samples where the oil sample to be tested is taken directly from a sample bottle without dilution. In such cases, a mechanically controlled syringe is typically used to draw up a measured volume of the liquid sample and inject it directly into the inlet port of the optical sensing cell of the optical particle counter. Alternatively, a sampling tube connected to the optical sensing cell inlet is lowered into the sample bottle. Pressure is used to force the liquid sample through the optical sensing cell of the optical particle counter. Samples are typically processed one by one (i.e., not in a batch process), with the optical sensing cell and feeding tubes being cleaned with solvent between tested samples.
Where liquid sample to be tested by optical particle counting are to be diluted prior to such testing in the prior art, it is common to manually measure and mix known quantities of the liquid sample and of a suitable diluent prior to testing. More specifically, a laboratory pipette is often used to manually draw a quantity of liquid from each sample bottle, as measured against volume markings on the pipette, and to inject this drawn quantity of liquid sample from the pipette into a sample container. This process is then repeated by pipette for adding a measured volume of a suitable diluent to the sample container. The two volumes are then summed for purposes of use in any subsequent calculations required to convert raw particle counts taken from a sample into standardized volumetric particle counts.
Although manual pipetting is accurate, it has a number of significant drawbacks associated with it, particularly where carried out repetitively for a high number of liquid samples to be subsequently presented for testing by an optical particle counter. These problems include, without limitation: i) pipetting is labour intensive (i.e., time consuming) for the operator carrying out the procedure; ii) pipetting is tedious for the operator carrying out the procedure; iii) the preparation of test samples cannot be performed outside of normal laboratory operation hours without special (and typically more expensive) arrangements being made to staff the test facility with appropriate laboratory personnel; and, iv) operators carrying out the pipetting procedure for large numbers of test samples are susceptible to repetitive strain injuries.
In order to improve and standardize methods for optical particle counting utilizing diluted liquid samples, ASTM International of West Conshohocken, Pa., USA has developed and published a test protocol known as ASTM-D7647 and entitled “Test Method for Automatic Particle Counting of Lubricating and Hydraulic Fluids Using Dilution Techniques to Eliminate the Contribution of Water and Interfering Soft Particles by Light Extinction”. ASTM-D7647 prescribes a standardized testing methodology that requires the use of a diluent to dilute the original samples to specified ratios of oil to diluent, prior to optical particle counting readings taking place. It has been found that the ASTM-D7647 test protocol notably addresses the particle count inaccuracy issues caused by particle coincidence and soft particles (as discussed above), especially where high viscosity liquids are being tested. Accordingly, the erroneous contribution of soft particles to the particle size cumulative count is substantially negated by the ASTM-D7647 methodology. The quality of particle count data is significantly improved on many samples as the effects of known interference are removed. The present invention discloses and claims, in its simplest non-limiting terms, a system for the automatic dilution and delivery of a plurality of liquid test samples to an optical particle counter for batch testing of diluted liquid samples according to ASTM-D7647 in a more accurate and efficient manner than has been possible with prior art sample handling equipment and methodologies.
In spite of the fact that ASTM-D7647 test protocol provides significantly more accurate automated optical particle counts than earlier testing methods, it has not gained widespread commercial acceptance. This lack of widespread commercial acceptance is thought in large part to stem from the fact that while the injection of the test sample into the optical sensing cell and the reading of particle counts by the optical sensing cell may be substantially automated through the use of existing equipment, the preparation and presentation of the test samples, including the addition of the aforesaid diluent (by prior art manual pipetting techniques), has not been significantly automated to date, and remains extremely labour intensive. In other words, the testing of diluted oil samples using the ASTM-D7647 protocol is presently known to be used only with manual sample presentation procedures, which include pipetting, as aforesaid, with all of the attendant problems and difficulties previously mentioned. As such, while ASTM-D7647 is able to obtain improved particle count results over earlier testing methodologies which do not involve the addition of a diluent to the original sample volume to be tested, the prior art drawbacks associated with pipetting, represent an ongoing limitation to its widespread commercial acceptance, particularly in light of the fact that the number of pipetting operations per sample tested has necessarily been doubled over prior methodologies not utilizing sample dilution.
Apart from manual pipetting of samples and diluent as discussed above, there is presently no known apparatus, system, or method for reliably automating the dilution and delivery of liquid samples of oils and hydraulic fluids to an optical particle counter, in accordance with the ASTM-D7647 test protocol.
It is therefore an object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter in compliance with the ASTM-D7647 testing protocol.
It is a further object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter in a manner that eliminates the need for manual pipetting of the liquid samples or of any diluents added to such liquid samples before such testing.
It is a further object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, wherein presentation of such mixtures for automated testing is less labour-intensive than with known prior art equipment and methods used for this purpose.
It is yet another object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, wherein The system permits for much more prompt and uniform presentation of such mixtures for testing on a batch process basis.
It is still an object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, wherein The system precludes the operator performing the preparation of such mixtures from becoming unduly fatigued or from incurring repetitive strain injuries.
It is also an object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, wherein The system permits comparable testing accuracy to prior art manual dilution methods that use a pipette.
It is yet another object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, which apparatus permits an accurate automated determination of the volume of the liquid sample and of any diluent required to be added to said sample in order to provide for automated filling of each said test container to a standard test volume prior to commencement of said automated testing.
It is yet another object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, which apparatus permits automated dilution of the liquid samples to be tested, especially new and used oils, in the higher viscosity ranges.
It is yet another object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, the construction of which apparatus is relatively simple, compact, and economical.
It is yet another object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, which system saves the time and expense of manual sample presentation methods which make uses of pipetting, and which presents the mixtures in an ordered array, so as to allow automated testing of the presented liquid samples without the need for additional manual manipulation or supervision of the mixtures during said automated testing, thereby permitting such testing to run outside of normal laboratory operational hours.
It is yet another object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, which system maximizes the effective capacity of operators by freeing them from the need for manual pipetting of liquid samples.
It is yet another object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, which apparatus precludes operators from experiencing repetitive strain injuries by reason of the elimination of pipetting tasks associated with such presentation in the prior art.
It is yet another object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, which system permits the dilution and delivery of a plurality of mixtures of diluent and liquid samples contained in congruent sample containers to an optical particle counter, in accordance with the ASTM-D7647 test protocol.
It is yet another object of the present invention to provide an improved system for reliably automating the dilution and delivery of a plurality of mixtures of diluent and liquid samples respectively disposed in an equal plurality of congruent sample containers to an optical particle counter, which system facilitates and promotes the adoption of the ASTM-D7647 test method on a more widespread commercial scale.